Tag Archives: PTFE

How to Investigate Compression Packing Failure Modes

Over-tightening, excessive speed and improper installation can cause a system to falter.

In many respects, troubleshooting and failure analysis of compression packing materials is similar to the investigation of a crime scene. A good investigator knows how to gather clues from many different sources and put them together to understand what has happened. A good troubleshooter uses the same information gathering method, familiarizing themselves with the sealing materials, the process equipment and the systems where they are used.

Start by Interviewing Witnesses

The troubleshooter should seek information from the people who work with the equipment on a regular basis. Seal installers, maintenance personnel, operators, process engineers and others can all shed light on potential causes of failure. Some key questions should be:

  • How is failure defined? Some examples include excessive leakage, overheating, high rate of flush water consumption, excessive friction load and blowout.
  • Is this application the source of chronic seal failures, or was this an unexpected event?
  • Were there any changes to the seal material, the equipment or the overall process that preceded the failure?
  • Were there any system upsets or cleaning cycles that preceded the failure?
  • Can you describe the installation procedure?

Gather Information About the Victim

Knowing the limitations of the sealing product is a key step. The acronym “STAMPS” will help remember the key elements to ensure the right packing is selected for the application.

  • S: Size. Is the correct packing cross-section being used? Are the rings cut or formed to the correct length?
  • T: Temperature. Check the system temperature against the packing manufacturer’s established temperature ratings for the product.
  • A: Application. Some packings are made specifically for rotary equipment while others are intended for valves or static seals. Check to make sure the packing is suitable for the equipment where it is being used.
  • M: Media. This refers to the fluid being sealed. Check with the manufacturer or with compatibility charts to be sure the seal material is compatible with the media. If the media is slurry, abrasion-resistant materials may need to be specified. If the media is toxic, explosive or required to be contained within certain maximum allowable leakage requirements, then a packing must also be selected on the basis of its ability to seal at low leakage levels.
  • P: Pressure. Check the system pressure against the packing manufacturer’s established pressure ratings for the product.
  • S: Speed. Check the equipment speed against the packing manufacturer’s established surface speed ratings for the product. Surface speed is expressed in feet per minute or meters per second and not revolutions per minute.

Investigate the Crime Scene

When possible, observe the equipment while it is running. Can you see, hear, feel, smell or use a sensor to make observations? Smoke, vibration, grinding noises, the scent of burning fibers and system pressure fluctuations are only a few of the clues that can be noticed or measured while the equipment is up and running.

Examine the condition of the equipment. Most packings are robust seals that can handle less than perfect equipment condition, but there are limits to the amount of degradation they can withstand.

Valve stems and pump shafts or sleeves should be checked for scratches, corrosion pitting and general surface roughness. Rough surfaces can damage the sealing surface and result in excessive leakage and quick wear of the seal.

Extrusion of the seal material
Image 1. Extrusion of the seal material

Excessive clearances at the top or bottom of the stuffing box can lead to extrusion of the seal material and intrusion of large solid particle into the seal area (see image 1).

In severe cases, excessive clearance may result in a seal blowout.

Most packings are not meant to function as both a seal and a bearing. In rotating equipment, poor bearing condition may result in shaft runout that “wallows out” the inside diameter of the seal. Misalignment may result in shaft/stuffing box offset that causes one side of the packing set to be heavily compressed while the other side is compressed much more lightly. A similar side loading of a packing set can occur in large horizontally oriented valves where the packing is forced to bear the weight of the stem.

Check to make sure all the parts are in place. During the breakdown, repair and reassembly of equipment it is possible to misplace parts. Equipment might be put back into service without seat rings, bushings, lantern rings, O-rings and other parts that are essential to proper equipment operation.

Look at the seal and the equipment as a part of a big picture.

Consider how this piece of equipment is affected by other equipment and control devices in the system. For example, is there a downstream valve that creates pressure spikes in an upstream pump seal when the valve closes and the pump is still operating?

Continue reading How to Investigate Compression Packing Failure Modes

The Perfect Wave; The Gerromatic Rotary Seal

Gear motors, pumps and stirring units keep process material in constant motion in the process industry’s production facilities. A large number of shaft seals are used at drive shafts to keep liquids securely within the equipment. But leaks may be more likely to occur if the pressure acting on the seals becomes too great. Freudenberg Sealing Technologies has developed a new rotary seal, the Gerromatic, which has a wave-shaped sealing lip. This increases the maximum amount of pressure that can be applied. The sinusoidal contact path also reduces friction and provides self-cleaning, which extends operating life.

In the process industry, including the food and beverage sector, shaft seals used in equipment mostly have a rotation-symmetrical seal lip, which abuts the rotating shaft with a groove-like contact pattern. During wet-running, this can cause the medium to be displaced at the contact surface. The seal then runs in a more or less dry condition, leading to increased friction and higher temperatures. The increased friction increases wear and reduces the efficiency of the equipment. The accompanying rise in temperature is not desirable, especially when the process media are temperature-sensitive. If the seal lip is also exposed to high temperatures at high rotational speeds – for example, due to a process material that applies pressure to the seal lip in a vessel with a stirring unit below it – the lip can fold down on the low-pressure side, which would result in immediate leakage and the seal’s failure.

Continue reading The Perfect Wave; The Gerromatic Rotary Seal

What is ePTFE?

ePTFE - Bill Gore & his wife, VieveSince 1958, Gore has developed products that improve lives. At the center of these solutions is polytetrafluoroethylene (PTFE), a polymer with exceptional properties like high tensile strength, a low dielectric constant, UV resistance and many more. In 1969, the possibilities for PTFE expanded with Bob Gore’s discovery of expanded PTFE, or ePTFE.

In the years since, Gore has developed unparalleled expertise in manipulating ePTFE and other fluoropolymers. Gore’s engineers can change a material’s structure, shape, thickness and surface geometry, then pair it with complementary materials to provide the performance qualities required by the application and the customer. The resulting product can be strong or permeable, rigid or flexible, thin or thick — with many additional combinations of properties that can be applied to meet the end use requirements.

Since its very founding, Gore has been passionate about solving the complex challenges of their global customers. From the first suggestion of a product need, to its delivery to market, this passion is apparent in everything Gore does.

  • Curiosity: From keeping water off a person’s skin to preventing leaks from happening in chemical containers, Gore listens to their customers and analyze the challenges to determine the underlying problem.
  • Competency: Gore determines how they can apply their expertise in fluoropolymer science to deliver solutions that are valued and differentiated from the competition.
  • Commitment: Gore rigorously tests their products to ensure they deliver failure-free performance and suit their customers’ needs and applications, the first time and every time.

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FDA Standards Key to Proper Gasket Selection

Food and beverage producers rely on a wide array of equipment to ensure their products are safe and free of contamination. Sealing devices such as gaskets are key components in this equipment, yet do not receive the attention they warrant given the critical importance of their function.

Gasket Selection - PTFE
PTFE (Polytetrafluoroethylene) Molecule

PTFE-based and elastomeric seals have for decades been the products of choice for food and beverage applications. The two most commonly referenced Food and Drug Administration (FDA) standards for sealing products are found in the Code of Federal Regulations under Title 21 (Food and Drugs), part 177 (Indirect Food Additives: Polymers). Section 177.1550 focuses on perfluorocarbons such as PTFE- based products, and Section 177.2600 deals with rubber articles intended for repeated use.

These two standards specify which ingredients used in the production of sealing products are acceptable for applications where contact with food products can occur, as well as how much of the approved ingredients can be released from the polymer/elastomer when extracted with specific media — i.e. water, hexane, etc. — under specified testing conditions.

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Pipe Gaskets for Diverse Flange Materials

Looking to consolidate your inventory into as few materials or parts as possible?  Would eliminating the installation of incorrect gasketing material interest you?  GORE® Universal Pipe Gaskets may be the answer.

GORE Universal Pipe Gaskets (UPG)GORE® Universal Pipe Gaskets (Style 800) provide a reliable seal for steel, glass-lined steel and fiber reinforced plastic (FRP) flanges, in the full spectrum of strong acid, alkali, and solvent process media, including the most challenging thermal cycling and elevated temperature applications. This single gasket solution can reduce the process safety and production downtime risks caused by the use of an incorrect gasket material. The highly conformable 100% ePTFE also reliably seals irregular surfaces.

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FFKMs Protect Components in Enhanced Oil Recovery

FFKMs, also known as perfluoroelastomers, were first developed in the 1960s for applications involving high temperatures and/or aggressive chemicals.  Perfluoroelastomers exhibit many properties similar to PTFE (polytetrafluoroethlyene, or Teflon®), and are considered inert in almost all solvents.  However, PTFE is a plastic, and when compressed, it will not recover to its original shape.  On the other hand, elastomers contain crosslinks, which act as springs to give the material resiliency and the ability to recover after a part has been compressed – this resistance to permanent compression gives the material the ability to maintain a seal over time. (To learn more about perfluoroelastomers, download our Introduction to Perfluoroelastomers White Paper).

The article below was recently published on FlowControlNetwork.com, and discusses how FFKMs are being used in oil & gas exploration, as production companies are increasingly operating in high-pressure, high-temperature (HPHT) downhole conditions.


HOW FFKMS PROTECT COMPONENTS IN ENHANCED OIL RECOVERY OPERATIONS

Companies are increasingly operating in high-pressure, high-temperature downhole conditions.
Enhanced oil recovery uses gas, steam or chemical injection to improve flow rate. All graphics courtesy of AGC

Improving technologies and methods to increase the recovery of oil from existing reservoirs is a global challenge. In the U.S., oil production at reservoirs can include three phases: primary, secondary and tertiary (or enhanced) recovery. The U.S. Department of Energy (DOE) estimates that primary recovery methods — which rely on the natural pressure of the reservoir or gravity to drive oil into the wellbore, combined with pumps to bring the oil to the surface — typically tap only 10 percent of a reservoir’s oil. Furthermore, secondary efforts to extend a field’s productive life — generally by injecting water or gas to displace oil and drive it to a production wellbore — still only push recovery totals to between 20 and 40 percent of the original oil in place. Clearly, much untapped oil and gas remains in existing wells.

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GYLON EPIX™ Reduces Gasket Installation Issues

GYLON EPIX™ is a newly developed family of PTFE gaskets. It is manufactured using a patented, profiled surface based on our proven Fawn, Off-White, and Blue GYLON® to create highly conformable materials for optimum sealing performance.

Watch the video below to learn more about GYLON EPIX™, and how it’s patented
hexagonal surface profile can help you reduce gasket installation issues.

GYLON EPIX™ will provide superior functional performance by combining the traditional attributes of GYLON® with an innovative surface design. It offers a broader range of applications than traditional PTFE gaskets that are used in worn and pitted flanges. In addition, this evolutionary material delivers the tight sealing and load retention properties of 1/16” (1.6mm) and the conformability of 1/8” (3.2mm). The hexagonal profile provides GYLON EPIX™ - 3504 EPXimproved compressibility and recovery. The profiled surface reduces the contact area during initial compression to concentrate the compressive force of the flange for improved sealability.

Designed for increased compressibility, GYLON EPIX™ improves performance in misaligned flanges. The consolidation of two thicknesses to one reduces the need to inventory multiple thicknesses. Garlock is dedicated to providing real sealing solutions that meet real world sealing needs. With an improved design, color-coded materials, and single thickness, GYLON EPIX™ makes sealing easier.

For additional information about specific GYLON EPIX™ products:

GYLON EPIX™ Style 3500 EPX

GYLON EPIX™ Style 3504 EPX

GYLON EPIX™ Style 3510 EPX

Form-in-Place Sealex® Joint Sealant

Sealex®Sealex® joint sealant, specially processed, 100% pure PTFE on a roll, provides soft, highly compressible gasketing for longer life and trouble-free sealing. Its form-in-place versatility also cuts maintenance and storage costs. The high compressibility of Sealex® enables it to effectively fill flange imperfections for a tight, leak-free seal. Under pressure, it provides a very wide, thin ribbon-like joint sealant. Unlike conventional PTFE which is prone to cold flow, Sealex® has good creep resistance and bolt torque retention properties.

Sealex® joint sealant does not support bacterial growth or cause product contamination and is FDA compliant. It has virtually no shelf-life concerns since PTFE is unaffected by normal environmental conditions.

It has excellent resistance properties to chemical attack. It is ideal for most chemical services at temperatures to 500°F (260°C) and pressure to 2,000 psi (138 bar). It is also suitable for cryogenic use to -321°F (-196°C).

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Proven Seal Design, New Materials

The Freudenberg Simmerring has been a successful product for about 85 years. It seals rotating shafts reliably, and is used in millions of applications and machines in many industries. The Simmerring is flexible, highly loadable, and very dependable. Freudenberg Sealing Technologies has now further developed Simmerrings for use in the process industry – and they are made of food-grade materials.

At high rotational speeds and pressures, traditional PTFE shaft seal rings quickly reach their limits. Seal malfunctions and leaks are the result. Moreover, it has not been possible to use Simmerrings in the food industry to this point because their PTFE materials have not been approved for food-related applications. That’s why experts at Freudenberg Sealing Technologies have developed two new materials – from which tried-and-tested Simmerrings are manufactured – especially to meet the process industry’s requirements.

Maximum Performance even under Extreme Pressure: B2PT

Food-Grade SimmerringsSimmerrings with the B2PT design can be stressed with pressures of up to 10 bar. The B2PT consists of a newly developed material, Quantum® PTFE F18245, and a housing made of 1.4571 (V4a) stainless steel. The PTFE used here has been conceived especially for direct contact with foods. The still-required approvals under FDA 21 CFR §177.1550 und EC 10/2011 are in preparation. This Simmerring design is thus superbly suited for the food and pharmaceutical industries. The design of the B2PT can also be adapted for customer-specific, individualized applications.

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PTFE as a Sealing Material

Polytetrafluoroethylene (PTFE) is commonly known as a coating for pans under the DuPont trade name Teflon™. It is also superbly suited as a sealant and is superior to many materials in specific ways. For example, it can be used at low and high temperatures and in combination with gasoline, solvents, water and other polar media such as lyes, standard lubricants and brake fluid. PTFE’s chemical resistance is nearly universal.

History

In 1938, while working for DuPont, American chemist Roy Plunkett was looking for a substitute for the fluorohydrocarbon Freon, which his employer was only allowed to sell to General Motors’ Frigidaire division for patent-related reasons. For his research, he had obtained a supply of tetrafluoroethylene (TFE), which was used as refrigerator coolant. He stored it in small pressurized gas cylinders at low temperatures. When he was ready to use the gas after a fairly long storage period, none was left in the container. But its weight was unchanged. After it was opened, there were white crumbs inside and the inner walls of the container were covered with a thin layer. Plunkett quickly realized that the TFE gas had been polymerized into a plastic. This new plastic, PTFE, proved to be completely resistant to chemical exposure. Not even aqua regia¹ could harm it in any way. But its production was so costly that practical uses seemed inconceivable.

PTFE - Used As a Coating on Fishing Lines Continue reading PTFE as a Sealing Material